The invention relates generally to a method of fabricating a semiconductor device and, more particularly, to a method of fabricating a semiconductor device, in which although a metal layer is included in a gate pattern, the gap-fill characteristic of contact plugs coupled to junctions can be improved and degradation in the data retention characteristic can also be prevented.
As the degree of integration of semiconductor devices increases, there is a tendency to miniaturize various patterns constituting the semiconductor devices. Such miniaturization of the patterns causes an increase in the resistance value of conductive patterns included in the semiconductor devices, which limits the degree of integration attainable for the devices. To overcome this limitation, a method of utilizing a metal layer of low resistivity, such as tungsten (W), as the conductive pattern has recently been introduced.
In the case in which a metal layer is used as the gate pattern of a NAND flash memory device in which a gate insulating layer, a floating gate electrode, a dielectric layer, and a control gate electrode are sequentially stacked, the metal layer is formed on a polysilicon layer for a control gate electrode. Thus, the control gate electrode comprises a stack structure of a polysilicon layer and a metal layer. To form the gate patterns of this structure, first, a dielectric layer, a polysilicon layer for a control gate electrode, and a conductive layer are sequentially formed over a semiconductor substrate in which a gate insulating layer, a polysilicon layer for a floating gate electrode, and an isolation layer are formed. The conductive layer, the polysilicon layer for the control gate electrode, the dielectric layer, and the polysilicon layer for the floating gate electrode are then etched to form gate patterns. At this time, the sidewalls of the gate patterns are damaged by the etching process, so a re-oxidization process for removing the damaged portions must be performed so as to prevent degradation of data retention characteristics of the semiconductor devices. However, there is a possibility that failure of the semiconductor device may occur, since the conductive layer expands abruptly due to heat used for the re-oxidization process and is abnormally oxidized. If the conductive layer is used, the re-oxidization process is difficult to perform. As a scheme for solving this problem, there has been proposed a selective oxidization process of oxidizing only the sidewalls of the polysilicon layer. However, although the selective oxidization process has been introduced, the data retention characteristic degradation problem of the semiconductor device remains unsolved.
Meanwhile, after the gate patterns are formed, junctions are formed in the semiconductor substrate on both sides of each of the gate patterns, and a pre-metal dielectric layer is formed over the semiconductor substrate including the gate patterns and the junctions. Next, contact holes through which the junctions are exposed are formed in such a way as to penetrate the pre-metal dielectric layer. The insides of the contact holes are gap filled with conductive material, thus forming contact plugs. Metal wiring lines electrically connected to the junctions through the contact plugs are formed on the pre-metal dielectric layer. In this case, the contact plugs can be stably formed only when no voids remain therein in the process of gap-filling the contact holes with the conductive material. In order to easily gap-fill the contact holes with the conductive material without the occurrence of voids, the aspect ratio of the contact hole must be low. However, the width of the contact hole decreases due to the high degree of integration. Moreover, if the conductive layer is used, the aspect ratio of the contact hole increases significantly since the height of the contact hole increases up to the height (i.e., thickness) of the conductive layer. Consequently, a problem arises because the contact holes are not fully gap-filled with the contact plugs.